Conventionally, in a DC-DC converter that executes control to equalize a DC input voltage with a reference voltage, a pulse width modulation (hereinafter, PWM) method in which a pulse width is controlled by maintaining a frequency of a signal that turns on a switching transistor constant, and a pulse frequency modulation (hereinafter, PFM) method in which a frequency is controlled by maintaining a pulse width constant have been known.
There is also a technique that executes control by the PWM method at the time of a heavy load, and switches to control by the PFM method that can reduce the number of switching operations of the switching transistor at the time of a light load. However, even in the PFM method that suppresses power consumption, a comparator that operates by a steady current is generally used in order to monitor a load condition. Therefore, there is still a room for improvement in suppressing power consumption by the comparator and increasing the conversion efficiency.